572 



CANADIAN EQUIVALENTS. 



[Ch. XXVII. 



because they contain certain species, -such, as Asaphus (Isotelus) gigas, 

 Illcenus crassicauda and Orthoceras bilineatum, in common with, the 

 overlying Trenton Limestone.* But, according to Prof. Hall, the 

 Illcenus was erroneously identified, an error to which he confesses 

 that he himself contributed ; and on the whole these lower beds con- 

 tain, he thinks, a very distinct set of species, only 3 or 4 of them 

 out of 83 passing upwards into the incumbent formations.f 



Be this as it may, the Black River Limestone, No. 15, contains 

 certain forms of Orthoceras of enormous size (some of them 8 or 9 

 feet long !), of the subgenera Ormoceras and JSndoceras, seeming to 

 represent the Lower Silurian or Orthoceras limestone of Sweden. 

 Moreover, the general facies of the fauna of all these beds is essen- 

 tially similar. Another ground for extending our comparison of the 

 Llandeilo beds of Europe as far down as the calciferous sandstone is 

 derived from the researches of Sir William Logan in Canada, and the 

 study by Mr. Salter of the fossils collected by the Canadian surveyor 

 near the S.E. end of the Ottawa River, where one mass of limestone 



Fossils from Allumette Rapids, River Ottawa, Canada, 

 a Fig. 659. 



Ifaclurea Logani, Salter. 

 a. View of the shell. o. Its curious operculum. 



Fig. 660. encloses species common to all the beds from 



the Calciferous Sandstone (No. 18) up to the 

 Trenton Limestone (No. 14). In this rock, 

 the Asaphus gigas and other well-known Tren- 

 ton species are blended with the Maclurea 

 (fig. 659), a left-handed shell, considered by 

 Woodward as probably a massive heteropod, 

 a genus characteristic of the Chazy Limestone, 

 or No. 17 ; and Murchisonia gracilis (fig. 

 660) is another Trenton Limestone species 

 found in the same Silurian limestone of Cana- 

 da ; J while one of the most common shells in 

 it is the Raphistoma t (Euomphalus) uniangulatum, Hall, a species 

 characteristic in New York of the Calciferous Sandstone itself. On 

 the whole, if we identify the beds from the Black River Limestone 



Murchisonia gracilis, Hall. 



A fossil characteristic of the 

 Trentou Limestone. The 

 genus is common in Lower 

 Silurian rocks. 



* Soc. Geol. France, Bulletin, vol. iv. p. 651, 1847. 



f Hall ; Forster and Whitney's Report on Lake Superior, Pt. II., 1851 



X Logan, Report, Brit. Assoc. Ipswich, pp. 59, 63> 



